/**
 * A force directed graph layout implementation by liuchang on 2018/05/10.
 */
const CANVAS_WIDTH = 1000;
const CANVAS_HEIGHT = 1000;
let k;
let mNodeList = [];
let mEdgeList = [];
let mDxMap = {};
let mDyMap = {};
let mNodeMap = {};
export default function ForceDirected() {
  //generate nodes and edges
  for (let i = 0; i < 20; i++) {
    mNodeList.push(new Node(i));
  }

  for (let i = 0; i < 20; i++) {
    let edgeCount = Math.random() * 8 + 1;
    for (let j = 0; j < edgeCount; j++) {
      let targetId = Math.floor(Math.random() * 20);
      let edge = new Edge(i, targetId);
      mEdgeList.push(edge);
    }
  }
  if (mNodeList && mEdgeList) {
    k = Math.sqrt(CANVAS_WIDTH * CANVAS_HEIGHT / mNodeList.length);
  }
  for (let i = 0; i < mNodeList.length; i++) {
    let node = mNodeList[i];
    if (node) {
      mNodeMap[node.id] = node;
    }
  }

  //随机生成坐标. Generate coordinates randomly.
  let initialX, initialY, initialSize = 40.0;
  for (let i in mNodeList) {
    initialX = CANVAS_WIDTH * .5;
    initialY = CANVAS_HEIGHT * .5;
    mNodeList[i].x = initialX + initialSize * (Math.random() - .5);
    mNodeList[i].y = initialY + initialSize * (Math.random() - .5);
  }

  //迭代200次. Iterate 200 times.
  for (let i = 0; i < 200; i++) {
    calculateRepulsive();
    calculateTraction();
    updateCoordinates();
  }
  console.log(JSON.stringify(new Result(mNodeList, mEdgeList)));
}

function Node(id = null) {
  this.id = id;
  this.x = 22;
  this.y = null;
}
function Edge(source = null, target = null) {
  this.source = source;
  this.target = target;
}

/**
 * 计算两个Node的斥力产生的单位位移。
 * Calculate the displacement generated by the repulsive force between two nodes.*
 */
function calculateRepulsive() {
  let ejectFactor = 6;
  let distX, distY, dist;
  for (let i = 0; i < mNodeList.length; i++) {
    mDxMap[mNodeList[i].id] = 0.0;
    mDyMap[mNodeList[i].id] = 0.0;
    for (let j = 0; j < mNodeList.length; j++) {
      if (i !== j) {
        distX = mNodeList[i].x - mNodeList[j].x;
        distY = mNodeList[i].y - mNodeList[j].y;
        dist = Math.sqrt(distX * distX + distY * distY);
      }
      if (dist < 30) {
        ejectFactor = 5;
      }
      if (dist > 0 && dist < 250) {
        let id = mNodeList[i].id;
        mDxMap[id] = mDxMap[id] + distX / dist * k * k / dist * ejectFactor;
        mDyMap[id] = mDyMap[id] + distY / dist * k * k / dist * ejectFactor;
      }
    }
  }
}

/**
 * 计算Edge的引力对两端Node产生的引力。
 * Calculate the traction force generated by the edge acted on the two nodes of its two ends.
 */
function calculateTraction() {
  let condenseFactor = 3;
  let startNode, endNode;
  for (let e = 0; e < mEdgeList.length; e++) {
    let eStartID = mEdgeList[e].source;
    let eEndID = mEdgeList[e].target;
    startNode = mNodeMap[eStartID];
    endNode = mNodeMap[eEndID];
    if (!startNode) {
      console.log("Cannot find start node id: " + eStartID + ", please check it out.");
      return;
    }
    if (!endNode) {
      console.log("Cannot find end node id: " + eEndID + ", please check it out.");
      return;
    }
    let distX, distY, dist;
    distX = startNode.x - endNode.x;
    distY = startNode.y - endNode.y;
    dist = Math.sqrt(distX * distX + distY * distY);
    mDxMap[eStartID] = mDxMap[eStartID] - distX * dist / k * condenseFactor;
    mDyMap[eStartID] = mDyMap[eStartID] - distY * dist / k * condenseFactor;
    mDxMap[eEndID] = mDxMap[eEndID] + distX * dist / k * condenseFactor;
    mDyMap[eEndID] = mDyMap[eEndID] + distY * dist / k * condenseFactor;
  }
}

/**
 * 更新坐标。
 * update the coordinates.
 */
function updateCoordinates() {
  let maxt = 4, maxty = 3; //Additional coefficients.
  for (let v = 0; v < mNodeList.length; v++) {
    let node = mNodeList[v];
    let dx = Math.floor(mDxMap[node.id]);
    let dy = Math.floor(mDyMap[node.id]);

    if (dx < -maxt) dx = -maxt;
    if (dx > maxt) dx = maxt;
    if (dy < -maxty) dy = -maxty;
    if (dy > maxty) dy = maxty;
    node.x = node.x + dx >= CANVAS_WIDTH || node.x + dx <= 0 ? node.x - dx : node.x + dx;
    node.y = node.y + dy >= CANVAS_HEIGHT || node.y + dy <= 0 ? node.y - dy : node.y + dy;
  }
}

function Result(nodes = null, links = null) {
  this.nodes = nodes;
  this.links = links;
}